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DNS SRV record

(also DNS Service record)

What is DNS SRV record?

A DNS SRV record is a type of DNS resource record that specifies the hostname and port number for a particular service within a domain. Unlike standard DNS records that only link domain names to IP addresses, SRV records provide essential details for applications like Voice over IP (VoIP) and instant messaging. They also include parameters like priority and weight to help clients choose among multiple servers. Additionally, SRV records can point to either A records for IPv4 addresses or AAAA records for IPv6 addresses, ensuring compatibility across network environments.

See also: See also: DNS query, DNS record, DNS A record, DNS AAAA record, DNS CNAME record, DNS MX record, DNS PTR record, DNS SOA record, DNS SPF record, DNS TXT record, DNS server, hostname, DNS server, DNS TTL

Components of SRV records

A DNS SRV record consists of several key components:

  • Service: The symbolic name of the desired service, such as sip for SIP or xmpp for XMPP.
  • Protocol: The transport protocol used by the service, typically either TCP or UDP.
  • Name: The domain name for which this record is valid, ending with a dot (e.g., example.com.).
  • TTL: The standard DNS Time to Live (TTL) field, which specifies how long the record should be cached by DNS resolvers.

DNS SRV record formats

_servicename._protocol.name. TTL class type priority weight port target.

  • servicename: The symbolic name of the specified service.
  • protocol: The transport protocol of the specified service, usually TCP or UDP.
  • name.: The domain name to which the record belongs.
  • TTL: DNS time to live field.
  • class: DNS class field, which is always IN.
  • type: The type of the record, which is always SRV for DNS SRV records.
  • priority: Shows the priority of the host. The lower the priority value, the more preferred the host is.
  • weight: A weight assigned for records with the same priority. If the value is higher, it is more likely that this record will be chosen.
  • port: The port on which the service will be located within the target server, which can either be TCP or UDP.
  • target.: The canonical name of the target server.

Why do you need an SRV record?

SRV records are essential for various reasons:

  • Service discovery: They allow clients to discover services running on different hosts and ports, facilitating communication between applications.
  • Load balancing: SRV records can distribute traffic across multiple servers by specifying priority and weight, ensuring efficient load balancing.
  • Flexible configuration: They enable easy changes to service configurations without requiring updates to client applications, as clients can query for the most current information.
  • Support for multiple protocols: SRV records accommodate services that use different protocols, making them vital for applications like VoIP and instant messaging, which may require specific transport methods.
  • Simplified management: By centralizing service information in DNS, SRV records simplify network management and reduce the need for hardcoded addresses in application configurations.